Viral infections continue to cause serious health problems, despite the existence of vaccines for some viruses. Vaccines have not been developed for a large number of viruses, such as those causing the common cold and AIDS. Some viruses appear to be refractory to efforts to develop vaccines, thus other approaches to anti-viral therapy and phrophylaxis are needed.
Several techniques for inducing immunity to viruses, other than traditional vaccines have been explored. In one such technique, mammalian cells are engineered in order to create cellular immunity to HIV. A DNA construct is introduced into the cells which includes an HIV promoter and the sequence of a product which is toxic to the HIV-infected cells, such as poliovirus protein 2A. The HIV-infected cells are killed by expression of the toxic product using a virus activated promoter. In another such technique, a mutant viral capsid protein is used to interfere with viable virus production. These techniques are described in International PCT Application entitled "Intracellular Method of Inhibiting HIV In Mammalian Cells" by Baltimore et al (PCT/US90/01266). An article by David Baltimore entitled "Intracellular immunization" (Nature, vol. 335, p. 395, Sep. 29, 1988) discusses the therapeutic approach for using cells engineered pursuant to Baltimore et al to be virus-resistant.
The use of a dominant negative strategy to study protein function was described by Herskowitz in an article entitled "Functional Inactivation of Genes by Dominant Negative Mutations" (Nature, Vol. 329, p. 219, 1987). Trono et al applied this strategy to the inhibition of viruses in an article entitled "HIV-I Gag Mutants Can Dominantly Interfere with the Replication of the Wild-Type Virus" (Cell, Vol. 59, pp. 113-120, 1989). See also PCT/US90/01266. These articles teach mutagenesis or truncation of a gene to create "dominant negative" mutations. The proteins expressed by the mutant genes are defective but are still capable of interacting with wild-type monomers of the protein produced by another allele. Other references teaching the dominant-negative strategy include; U.S. Pat. No. 4,774,182 entitled "Partially Detective Foreign Gene for Conferring Immunity on a Biological Host" to Szybalski; an article by Malim et al entitled "Functional Dissection of the HIV-I Rev Trans-Activator-Derivation of a Trans-Dominant Repressor of Rev. Function" (Cell, Vol. 58, pp. 205-214, 1989); an article by Chejanovsky et al entitled "Mutation of a Consensus Purine Nucleotide Binding Site in the Adeno-Associated Virus rep Gene Generates a Dominant Negative Phenotype for DNA Replication" (Journal of Virology, 1990, pp. 1764-1770); an article by Green et al "Mutational Analysis of HIV-I Tat Minimal Domain Peptides: Identification of Trans-Dominant Mutants that Suppress HIV-LTR Driven Gene Expression" (Cell, Vol. 58, pp. 215-223, 1989); and an article by Friedman et al entitled "Expression of a Truncated Viral Transactivator Selectively Impedes Lytic Infection by Cognate Virus" (Nature, Vol. 335, p. 452, 1988).
Fusions of viral core or capsid proteins to other proteins, and the assembly of the fusion proteins into virus particles has been disclosed in the art. A patent by Kingsman et al entitled "Particulate Hybrid HIV Antigens" (U.S. Pat. No. 4,918,166) and related International PCT Applications (WO 88103563 entitled "Fusion Proteins and Particles" and WO 88103662 entitled "Particulate Hybrid HIV Antigens") teach fusions of an HIV antigen to the capsid protein of a retrotransposon or retrovirus. Self-assembly of virus or virus-like particles in the presence of the capsid protein/HIV antigen fusion produces a viral structure with the fused antigen incorporated into the capsid structure. A related paper by Gilmour et al entitled "A Novel Method for the Purification of HIV-1 p24 Protein from Hybrid Ty Virus-like particles (Ty-VLPs) (AIDS 1989, Vol. 3, No. 11) shows that the HIV antigen can be cleaved from the viral-like particle using activated factor Xa. Similarly, Weldon et al., Journal of Virology, vol. 64, pp. 4169-4179, 1990, teaches the cleavage and secretion of iso-l-cytochrome C from an RSV gag fusion protein. A paper by Kingsman et al entitled "Host-vector systems" (Trans. R. Soc. Lond. B324, pp. 477-485 (1989) teaches that a capsid/antigen fusion is assembled into virus-like particles in yeast which display the HIV antigen gene on the particle surface.
Various additional references teach the use of gene constructs to produce viruses with recombinant surface proteins: U.S. Pat. No. 4,593,002 entitled "Viruses with Recombinant Surface Proteins" to Dulbecco; and, an article by Jones et al entitled "Assembly of gag-.beta.-Galactosidase Proteins into Retrovirus Particles." These references teach the formation of fusion proteins which express their non-viral portions on the virus particle surface for use as vaccines and diagnostic uses.
Despite these advances in the art, there is still a need for new methods to combat viral diseases.